1. Field of the Invention
The present invention relates to a vehicle system which includes multiple paths extending in parallel, and vehicles each shuttling on a corresponding one of the paths.
2. Description of the Related Art
Conventionally, there is a device to automatically load and unload multiple articles onto and from racks used for vertically and horizontally placing and storing the articles. Such a device is introduced in Japanese Unexamined Patent Application Publication No. 11-59819 as an on-rail wheeled platform system, and is also referred to as a stacker crane.
The stacker crane is equipped with a transfer device to transfer an article to load and unload the article between the racks. The entire stacker crane horizontally travels along the racks, and the transfer device vertically shuttles. Such a feature makes it possible for the stacker crane to transfer an article stored on any position of the racks. Here, a position of the stacker crane in a horizontal direction is detected by a laser range finding device. The detected data is transmitted to a central control system through optical wireless communication. Hence, the stacker crane is disposed at a desired position.
One of recently proposed vehicle systems includes shelf boards, a rack, rails, and vehicles. The shelf boards are vertically provided to the rack. The number of the rails is equivalent to that of the shelf boards, and each of the rails forms a path and is provided to a position corresponding to one of the shelf boards. Each of the vehicles is provided to one of the paths to horizontally transport an article. Such a vehicle system has a vehicle independently travel to each shelf board. Compared with the stacker crane, the system achieves significantly greater work efficiency in loading and unloading articles onto and from the racks.
In loading and unloading an article at a desired position of a rack, however, the vehicle system needs to measure a position for each of the vehicles in a horizontal direction, and transmit the measured data to each of the vehicles to control the vehicles. In other words, each vehicle has to have a laser range finding device and a communication device to exchange detected data. Here, a laser beam from the range finding device and light for the communication can cause interference with each other, which would increase the risk of an adverse effect to the communication and the distance measurement.
It is noted that in the following description, the language “interference” indicates not only physical interference of light but also simply indicates “an effect on distance measurement and communication”.